That 100% would not work. Chainmail didn’t have spell slots because wargames are single encounter battles that typically last 3 to 4 turns. Role playing games are long format adventures where resource management plays a much greater role. If powerful spells aren’t a limited resource the game is just broken beyond fixing, because the solution to every problem becomes “fire another nuke until it’s dead.”
Powerful spells, agreed. What I was discussing was lesser functional spells being more wide use. As someone who has been playing a mage for 30 plus years, it becomes a joke that in every combat I am either a) throwing darts, b) ducking and covering, or c) VERY RARELY casting one of the 10 or so spells I have FOR THE DAY in the hopes that I don't need it for the next encounter.
I see no reason why mages can't throw minor spells in the same degree as fighters can attack. And given that a well equipped fighter of 5th level is getting 2-3 attacks per round and hitting for in excess of 10-15 points per hit, why can't wizards at least contribute to combat without having to carry around a sack of rocks or a bandolier full of pointy objects to supplement their casting?
Regarding Chainmail, you are right. No spell slots. So the original development of D&D adopted that. I am just saying that it hasn't continued to evolve to the same extent as other classes and abilities.
